In recent years, attention is being focused on the development of electric cars or hybrid cars that use a commercial power supply for a household or the like to charge a secondary battery mounted on the vehicles. This charging is performed using a charging cable. Attention is also being focused on use of this charging cable also for communication (power line communication system) between the home side and the vehicle side in addition to the use for charging.
There is a conventional power line communication system that transmits charging information regarding vehicle-mounted secondary battery from the vehicle to a home-side power line communication section via a charging cable. Furthermore, the conventional power line communication system is provided with a relay that shuts off power in the charging cable (e.g., Patent Literature 1).
There is also another conventional power line communication system that provides a bypass for a relay so that power line communication is made possible even when the relay provided in the power line is shut off (e.g., Patent Literature 2).